Patent GB-718690-A (GB)
Title: Improvements in and relating to electric lamp basing
IPC: H01J9/30
Filed: 1953-08-28
Abstract: 718,690. Capping electric lamps. BRITISH THOMSON-HOUSTON CO., Ltd. Aug. 28, 1953, [Aug. 28, 1952.] No. 23838/53. Addition to 718,686. Class 39 (2). [Also in Group XXII] In welding a leading-in wire to a metal part of a base or cap of an electric lamp, the leading-in wire is cut off to a short stub having substantial stiffness and positioned to provide a low resistance contact connection between the root of the stub and the metal part of the cap, the outer end of the stub being next contacted with a relatively massive electrode and a direct current having a drooping characteristic passed through the cap, stub and massive electrode, the circuit being so arranged that the said electrode is of negative polarity. In the example bulbs for electric incandescent lamps of the screw-threaded type are supported neck upwardly in workholders 4, each comprising a cup 8 at the upper end of a rod 7 which is pressed upwardly by a spring 9 to hold the upper end of the bulb neck within a cap 12 located between a pair of spring-controlled pivoted jaws 13, 14, Fig. 1 (not shown), upward movement of the cap being limited by a stop-plate 10 apertured to receive the central end button 11 of the cap. The work holders are mounted around the periphery of a turret machine which is indexed in known manner through a series of work stations and, at station A, a leading-in wire 19 extending laterally from between the neck of a bulb 3 and the lower rim of the cap 12 is located between a pair of automatically operated scissorstype cutters 21, 22, which are held apart during the indexing movements of the turret. The upper cutter 21 is fixed upon a bracket 23 on a standard 24 mounted on the machine frame, the lower cutter 22 being secured upon a lever 26 actuated by a cam-controlled connecting rod 28, the operation being such that the wire is sheared off to within about one-eighth of an inch from the cap, whereupon a slight further upward movement of the lower cutter is effected so that a projecting lip thereon bends the remaining stub of wire upwardly slightly above the horizontal to achieve a good mechanical contact with the shell of the cap. The bulb is next indexed to work station B, Fig. 3, where it is disposed opposite a comparatively massive electrode 31 mounted on a plate 33 forming part of a parallel link system comprising a crank 34 hinged to a bracket 37 secured on a stationary frame member 25, and a bell-crank 38 hinged to a bracket 37a and fastened to a vertically reciprocable connecting-rod 42. The connecting-rod, which is actuated by a cam lever 43, is formed in two parts linked together through a sleeve 45 and a pair of tension springs 46 connected between transverse pins 47, 48 in the ends of the upper and lower parts of rod 42, the pin 47 being free to ride in a slot 49 in the sleeve, thereby providing a lost motion after the electrode 31 has been swung forward into contact with the stub wire 19. The welding circuit is completed by a roller 51 which is rotatably mounted at the lower end of an inclined pivoted rod 52 and pressed resiliently against the metal edge of the cap. To provide a welding current having a drooping characteristic a condenser 63 of relatively high capacity, e.g. 2,500 microfarads, is connected across a D.C. source such as a full-wave bridge rectifier 65 and the positive terminal is connected to the roller 51, the negative terminal being connected to the electrode 31 through a rheostat 64. An initial heavy current which flows when the electrode 31 contacts the stub 19a of the leading-in wire produces a small molten sphere which ultimately becomes welded to the rim of the cap without the addition of welding metal from an extraneous source. The method may be adapted to weld the top leading-in wire of the lamp to the end contact or eyelet.